Semiconductor resistor and photoconductive assembly containing same



d- 1969 H. J. M. JOORMANN ET AL 3,475,713

SEMICONDUCTOR RESISTOR AND PHOTOCONDUCTIVE ASSEMBLY CONTAINING SAME Filed June 7:, 1967 2 Sheets-Sheet l FIG. 1

29 32 41 45 35 50 FIG. 2

INVENTORS HENDRIK J.M. JOORMANN AALBERT VAN VULPEN H. J. M. JOORMANN ET AL 3,475,713 SEMICONDUCTOR RESISTOR AND PHOTOCONDUCTIVB ASSEMBLY CONTAINING SAME Oct. 28, 1969 Filed June 5, 1967 2 Sheets-Sheet 2 INVENTORS HENDRlK .LM. JOORMANN AALBERT VAN VULPEN United States Patent M US. Cl. 338-17 5 Claims ABSTRACT OF THE DISCLOSURE A substantially prismatic shaped semiconductor resistor having at least one side face bevelled up to an end face which end face lies at right angles to the other faces of the resistor body, the bevelled side face and the opposite side face being provided with metal electrodes which extend up to the end face. Such a resistor may be mounted on a printed circuit board with the bevelled end away from the circuit board.

The invention relates to a semi-conductor resistor having a body of semiconductive material which is preferably sintered and comprises electrodes and to a method of manufacturing such a resistor. Examples of such resistors are photoresistors, thermistors and varistors.

For many applications it is necessary to have semiconductor resistors which have characteristic properties which can be obtained only by a very small electrode separation. According to the conventional methods of manufacturing the said semiconductor resistors, the electrodes are juxtaposed on the same surface of a semiconductor body. If, however, this has to be done with a very small mutual distance, it becomes difficult during providing the electrodes not to contaminate or damage the semiconductor material between the electrodes and to hold the spreading between various specimens within admissible limits. As a result of this the manufacturing cost of such resistors becomes comparatively high.

It is the object of the invention to provide a reliable semiconductor resistor of the above type which has a small electrode distance and which can be manufactured economically.

According to the invention, a resistor of the above type is characterized in that the shape of the body is substantially prismatic, at least one of the side faces of said body being bevelled near one end up to an end face which extends at right angles to the side faces of the body and is constituted by a surface of fracture of the material, said bevelled side face and an oppositely located side face each being provided with a metal coating serving as an electrode and extending up to the edge of the said surface of fracture. Such a resistor may have a very small, readily reproducible distance between the electrodes mutually while the surface of fracture constitutes a non-contaminated surface of semiconductive material located between the electrodes. The resistor may be used without additional measures for being mounted on a printed circuit board if the side faces with the electrodes at the end remote from the bevelled end are located at a mutual distance corresponding to the pitch of said wiring and the last-mentioned end comprises a surface which extends at right angles to the side faces. The characteristic properties of a resistor according to the invention are mainly determined by the region where the electrode separation is smallest. In a photoconductive resistor according to the invention, for example, the dark resistance thereof is sub- 3,475,713" Patented Get. 28, 1969 stantially not influenced by the part of the resistor which is not located in the proximity of the surface of fracture which is then used as the photosensitive part, because the electrode separation there is large everywhere with respect to that of the surface of fracture.

In a further elaboration of the semiconductor resistor according to the invention fiat strip-like connection elements are provided on the metallized side faces while in a preferred embodiment thereof the connection elements extend at right angles to the surface of fracture with their longitudinal direction. As a result of the flat striplike connection elements a ready electric and mechanical connection of the said connection elements to the side faces is obtained. Because the connection elements extend with their longitudinal direction in the direction at right angles to the surface of fracture, a very compact arrangement becomes possible in a circuit arrangement in which such a resistor is used.

The invention further relates to a method of manufacturing a semiconductor resistor of the type mentioned 1 in the preamable. According to this part of the invention such a resistor is obtained by breaking a plate of semiconductive material which is metallized on oppositely located surfaces, the said plate being provided at least on one of these surfaces with a groove, the semiconductive material being broken at least along that groove.

It is known in the manufacture of selenium rectifier cells to provide grooves in a plate which is metallized on both sides and to break it along the grooves. As a result of this a small electrode separation along the surface of fracture is not obtained while in addition one of the electrodes cannot extend up to the surface of fracture as a result.

The method according to the invention is characterized in that the metal coating on the said surface is provided after providing that groove in that surface.

This method enables an economic manufacture of a resistor according to the invention. Because the metal coating is provided after grooves have been provided in the plate, the fracture along that groove automatically provides a surface of fracture along which the electrodes can extend at a very small mutual distance.

The invention will be described in greater detail with reference to the drawings showing a number of embodiments.

In the drawings which, for clearness sake, are not drawn to scale are shown:

FIGURE 1 in an isometric projection a semiconductor resistor according to the invention which is mounted on a partly shown printed circuit board.

FIGURE 2 shows partly in cross section, partly in isometric projection, a part of a reading matrix for punched tape information in which resistors according to the invention are incorporated which are provided with strip-like fiat metal connection elements.

FIGURES 3, 4, 5 and 6 show various stages of a method according to the invention.

Referring now to FIGURE 1, reference numeral 1 denotes a semiconductor resistor, for example, a temperature-sensitive resistor, according to the invention, which is suitable for being mounted on a printed circuit board. The .resistor 1 is mounted on a board 3 which is only partly shown and comprises printed wiring 5, 7. The resistor 1 consists of a substantially prismatic body 9 of approximately 1.25 x 1.25 x 3 mms. of a sintered semiconductive material.

This semiconductive material may, for example, be a lanthanum doped barium titanate having a positive temperature coefi'icient of its electrical resistance. For resistors having a negative temperature coefficient, the semiconductive material may be, for example, lithium doped nickel oxide or titanium doped ferric oxide. Near one end of the body 9, two oppositely located side faces 11 and 13 are bevelled. The bevels end in a surface of fracture 15 which extends at right angles to the side faces of the body 9. The side faces 11, 13 are each provided with a metal coating 17, 19, for example, of nickel-chromium deposited from the vapour phase. The metal coatings 17, 19 extend at one end up to the surface of fracture 15 and at the other end up to a second end face 21 located opposite to the surface of fracture 15. The second end face 21 bears on the plate 3 with printed wiring 5, 7 in such manner that the metal coatings 17, 19 bear on the conductors 5, 7 with their edges extending along the end face 21. The metal coatings 17, 19 are connected in an electrically conductive manner to the conductors 5, 7 along said edges, for example, by means of an electrically conducting cement as is diagrammatically shown and denoted by 23 and 25. On the surface of fracture, the distance between the metal coatings 17, 19 of the side faces 11, 13 serving as electrodes is smaller than at other areas of the resistor. This distance can easily be made beforehand to be a few hundred microns or smaller. The surface of fracture 15 is a non-contaminated surface. The properties of the resistor which are substantially determined by the properties of the semiconductive material in the surface of fracture or in the proximity thereof are consequently not influenced by impurities. The resistor 1 may alternately be constructed, for example, as a photosensitive resistor when, for example, the body 9 consists of copperand gallium-activated cadmium sulphide or cadmium selenide.

Other photosensitive semiconductor materials suitable for the body 9 are, for example, A B compounds, such as gallium arsenide and gallium phosphide.

Both the light and the dark resistance between the electrodes 17 and 19 are mainly determined by that of the surface of fracture 15. In all other places on the resistor, the electrode separation and consequently the resistance between the electrodes per surface unit thereof is much larger than in the surface of fracture so that the resistances of the other parts substantially have no influence on the properties of the assembly.

As shown in FIGURE 2 a number of photosensitive resistors 27, 29 according to the invention are mounted in holes 31 in an electrically insulated plate 33. The holes 31 are arranged regularly in rows and columns and have diameters, for example, of 1.1 mms. The centre distance between the successive holes in a row or column is, for example, 2.54 mms. The thickness of the plate 33 is, for example, 10 mms. and the plate consists of an electrically insulating light-absorbing material, for example, an opaque phenolic paper laminate. The resistors 27, 29 comprise a substantially prismatic body 32 of, for example, sintered copperand galium-activated cadmium sulphide, the dimensions of which are, for example, 1 x 1 x 5.5 mms. Two oppositely located side faces of the body 32 are provided with metal coatings 34, 35, for example, a layer of gold deposited from the vapour phase. The metallised side face 35 is bevelled and ends in a surface of fracture 37 which serves as a photosensitive surface. Strip-like flat metal connection elements 39, 41 are secured in an electricaly conductive manner, for example, with an electrically conductive cement, to the metal-coated side faces 34, 35. The Width of the strips 39, 41 may be equal to that of the holes 31 and the strips may extend in the longitudinal direction along the body at right angles to the surface of fracture 37. The connection element 39 comprises, at its end remote from the body 32, a curved portion 43 with which it bears on an electrically conductive layer 47, for example, of a conductive silver lacquer which is provided on the plate 33. The bent portions 43 are secured to the conductive layer 47 by means of an electrically conductive cement 48. The connection element 41 extends at one end to beyond the end of the body 32 remote from the surface of fracture 37 and, at the other end, to before the bevel of the metallised side face 35. The connection element 41 is somewhat narrowed at its end 45 remote from the surface of fracture 37. The narrowed ends 45 of the connection elements 41 of the resistors 27, 29 are connected in an electrically conductive manner, for example, by dip soldering, in sleeves 50 which are secured, for example, by folding, in an electrically insulating plate 49 of, for example, hard paper having a thickness of approximately 2 mms. The sleeves 50 contact soldering lugs 51 to which may be connected a separate supply conductor (not shown) for each individual resistor. Preferably before providing the resistors 27, 29, the plates 33 and 49 are glued together in their mutualy correct position after which the resistors 27, 29 are inserted into the holes 31 and cemented with their ends 43 to the layer 47 of the plate 33. The ends 45 are then soldered in the sleeves 50 by dipping the sides of the plate 49 remote from the plate 33 in a soldering bath. With the above described device a radiation pattern can be detected such as it has to b edone, for example, by a reading matrix in a reading punched card information.

The construction of the resistors according to the invention with the longitudinal direction of the connection elements at right angles to the surface of fracture and projecting on either side of the body enables a very compact structure of the matrix while nevertheless the price may be low as a result of the simple construction of the resistors.

In the above described reading matrix the measuring angle of the photoresistors is restricted by the deep location of the surfaces of fracture 37 in the holes 31 which does not require any costly measures as a result of the favourable construction of the photoresistors 27, 29.

FIGURES 3 to 6 show the manufacture of a semiconductor resistor according to the invention in various stages. A plate 53 (FIGURE 3) of sintered semiconductive material having a groove 55 is obtained by compressing a quantity of finely divided semiconductive material in a mould, the groove 55 being also formed by that mould, and then sintering the resulting plate.

Then (FIGURE 4) a conductive layer 57, 59, for example, of gold and deposited from the vapour phase, is provided on both sides. Then the plate is broken along planes denoted by broken lines 61 in a direction at right angles to the groove so that blocks as shown in FIGURE 5 are obtained. Each of these blocks is finally broken along the groove 55 according to a plane which is shown in broken lines 63.

FIGURE -6 diagrammatically shows the resistor obtained after breaking along a surface of fracture 65 along the groove 55. So the surface of fracture 65 is obtained at the end of the process so that the possibility of damage and contamination thereof is very small.

The depth of the groove 55 determines the minimum distance of the metal coatings 57, 59 on the surface of fracture 65 and thus mainly the electric properties of the resistor.

What is claimed is:

1. A semiconductor resistor having a body of a semiconductive material provided with electrodes, said body being substantially prismatic in shape with at least one side face being beveled near one end up to an end face of said body, said end face extending at right angles to the side faces of said body and being constituted by a surface of fracture of said semiconductor material, said beveled side face and the oppositely located side face being each provided with a separate metal coating, each of said metal coatings serving as a separate electrode and each of said metal coatings extending up to and ending at the edge of said surface of fracture.

2. A semiconductor resistor as claimed in claim 1, wherein flat strip-like connection elements are provided on the metallized side faces.

3. A semiconductor resistor as claimed in claim 2, wherein the connection elements extend with their longitudinal direction in a direction at right angles to the surface of fracture.

4. A photoconductive resistor of claim 3 wherein the fiat strip-like electrical connection element provided on a bevelled side face extends at most to but not beyond the bevel and the oppositely located connection element extends beyond the surface of fracture and terminates in an end curved away from said surface of fracture.

5. A photoconductive assembly, particularly useful as a reading matrix for reading punched card information, said assembly comprising in combination, a flat insulating plate, an electrically conductive layer positioned on one surface of said plate, said plate and electrically conductive layer being provided with a plurality of apertures, a strip-like electrical connection element positioned in a plane away from said insulator plate on the side opposite of the electrically conductive layer, a photoconductive resistor of claim 4 located between each aperture and said electrical connection element, each photoconductive resistor being positioned in such a manner that the surface References Cited UNITED STATES PATENTS 1,011,824 12/1911 Linder et a1 338-15 2,196,830 4/1940 Hewlett 338-15 2,678,401 5/1954 Jaeger 33817 X 2,823,245 2/1958 Solow 33817 X REUBEN EPSTEIN, Primary Examiner US. Cl. X.R. 

